1. Field of the Invention
The present invention relates to a power supply controller, and particularly relates to detection of a short-circuit anomaly of a semiconductor switching element.
2. Description of the Related Art
A power supply controller is conventionally provided for controlling power supply to a load. In the power supply controller, a high-power semiconductor switching element such as a power MOSFET is disposed on a current supply line connected between a power source and the load, and the power supply to the load is controlled by switching the semiconductor switching element between ON and OFF according to external ON and OFF signals.
In such a power supply controller, it is known that a self-protective function is provided for protecting its own semiconductor switching element. The self-protective function controls the potential of the control terminal (e.g., the gate in the case of a MOSFET) of the semiconductor switching element so as to turn off the semiconductor switching element when an overcurrent (i.e., an abnormal current) has occurred on the current supply line due to short-circuiting in the load or the like.
Specifically, a current detecting resistor is serially connected to the load terminal (e.g., the source or drain in the case of a MOSFET) of the semiconductor switching element as shown in JP-A-2001-217696. The load current passing through the semiconductor switching element is detected based on the voltage between the terminals of the resistor. When the load current value is larger than a predetermined threshold, an occurrence of an overcurrent anomaly is determined, and thereby the semiconductor switching element is turned off (i.e., turned to a shutoff state).
Short-circuiting could also occur in the semiconductor switching element for some reasons. Specifically short-circuiting may occur between input and output terminals (e.g., drain and source in the case of a MOSFET), or between input and control terminals (e.g., drain and gate in the case of a MOSFET) of the semiconductor switching element. In this case, power will be supplied to the load, even when the power supply controller receives an OFF signal.
That is, if a vehicle lamp is connected as a load to the power supply controller, for example, the lamp is on at all times due to the short-circuiting. The vehicle driver may know the short-circuiting from the lamp being on at all times. However, he/she hardly finds that the lamp is on particularly in the daytime.
Further a problem arises that the self-protective function will not operate due to the short-circuiting, even when an anomaly such as an overcurrent has occurred. Therefore the short-circuiting in the semiconductor switching element should be detected and determined as a short anomaly.